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efficient machining of wind turbine blades using pcd inserts

Rotor blades are the most prominent components of the wind turbine. Each wind turbine has three rotating blades which are typically made of glass fiber reinforced polymer (GFRP) or carbon fiber reinforced polymer (CFRP). These materials have a polymer matrix, made of epoxy, vinylester, or polyester thermosetting plastic, which is reinforced with glass (for GFRP), or carbon (for CFRP). Other materials used for reinforcement include carbon nano fibers and wood. Due to the abrasive and non-homogeneous nature of this composite material, polycrystalline diamond pcd inserts are used in combination with suitable milling cutters and drilling tools to effectively machine this material.

Machining composite non-ferrous materials like CFRP pose some unique challenges. First, the non-homogeneous nature of the material makes it difficult to achieve a smooth surface during turning, milling or drilling. Other issues that come up frequently during machining are delamination, splintering and shorter tool life. The following are the two major operations that are performed on the rotor blade.

Face Milling of the Open End
The circular end of the rotor blade needs to be milled before drilling the holes that will be used to attach it to the flange of the rotor hub. Since most modern wind turbines have three blades, an efficient milling cutter and polycrystalline diamond pcd insert like the square shaped SEGT insert with a high positive geometry should be used. Other inserts that may be used include the SEET and SEMT inserts. For fine finishing of the face milling, use the WEEW insert, a single-tipped insert with an efficient wiper.

Since pcd inserts permit higher feed rates and cutting speed, typical cutting speeds for carbon reinforced polymers should be between 100 and 300 m/min with a feed rate of 0.1 – 0.3 mm/tooth and cutting depth of 0.2 – 2 mm. For glass reinforced plastic, the cutting speed should be between 100 – 200 m/mm with a feed rate of 0.05 – 0.2 mm/tooth and a cutting depth of 0.2 – 2 mm. If there are signs of delamination after the finishing operation, reduce the feed rate. When splintering occurs, the speed and feed rate should be increased.

Drilling of Holes
The drilling of the rotor blade can be a long and tedious process which requires high precision and accuracy. Hence, indexable drilling cutters, that can accommodate indexable polycrystalline diamond pcd inserts, should be used to make the process faster and more productive. Some of the inserts used in drilling cutters include the hexagonal shaped WNMG insert. This insert has six cutting edges and it permits higher cutting speeds and feed rates. With a drill that can accommodate multiple inserts, the drilling operation may be completed without any need to change the inserts. Drilling of the open end of the rotor blade may also be performed with other inserts like the TNMG, DNMG, CNMG.

Conclusion
Machining the rotor blade of a wind turbine with polycrystalline diamond pcd inserts will help to overcome many of the challenges encountered when turning, drilling or milling non-metallic composite materials. PCD inserts also allow for higher cutting speeds so that the process can be done faster and more economically.

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